Draft controlling stack damper mechanism for conserving heat in furnaces



May 23, 1950 'r. J. MACKAY DRAFT CONTROLLING STACK DAMPER MECHANISM FOR CONSERVING HEAT IN FURNACES 2 Sheets-Sheet 1 Filed March 15, 1944 INVENTOR.

T. J. DRAFT CONTROLLING STACK DAMPER MECHANISM FOR CONSERVING HEAT IN FURNACES Filed March 15, 1944 MACKAY May 23, 1950 2 Sheets-Sheet 2 INVENTOR.

Patented May 23, 1950 DRAFT CONTROLLING STACK DAMPER MECHANISM FOR C IN FURNACES onsnnvmc HEAT Ted 3. Mackay, West Orange, N. J. Application March 15, 1944, Serial No. 526,611

3 Claims. (01. 110-163) This invention relates in general to means for conserving heat in heating apparatus, especially in furnaces employing 011 or gas as the heat generating medium; and more particularly the invention contemplates automatic mechanisms for restricting the escape of heated air through the flue or smokestack during the stand-by period; 1. e., when the heating unit such as an oil burner is at rest.

One object of the invention is to provide mechanism of the character described which shall embody novel and improved means for automatically restricting the flow of hot gases from the furnaces, for example, by the closing of the damper, after a predetermined time interval following the stopping of the heating unit sufllcient to permit complete purging of the furnace of poisonous and unburned combustible gases, whereby the accumulated thermal units in the hot air which is devoid ofobjectionable gases shall be retained in the furnace during the standby period to conserve heat. I am aware that certain devices intended to accomplish such results have been proposed, but the period allowed heretofore for purging of the furnace is inadequate.

Another object is to provide in such mechanism novel and improved means for automatically providing for free flow of gases from the furnace through the flue or smokestack, for example by the opening of said damper, a predetermined time interval of sufficient length prior to restarting of the heating unit, to allow the pressure of the hot gases in the furnace and of the cool air in the flue to become equalized to prevent puffback upon starting of combustion and also to permit escape of any objectionable gases that may have accumulated during the stand-by period.-

- Further objects are to provide in mechanism of the character described novel and improved timing mechanism for predetermining the time interval for free flow of gases through the flue prior to re-starting of the heating unit after a standby period; and thus to provide a novel and improved combination of an electric switch and timing means for closing it, which shall be simple, reliable and inexpensive and can be utilized as a circuit controller in many different electric circuits or apparatus.

Another object is to provide a novel and improved mechanism responsive to temperature of the hot combustion gases for controlling the operation of said means such as a damper for restricting escape of the hot gases from the furnace during the stand-by period, which shall be 2 I I positive in operation and simple and inexpensive in construction. i

A further object is to provide novel and improved means for automatically holding a barometric draft control device in closed position during the stand-by period and for automatically releasing said device prior to starting of the heating unit. I

Other objects are to provide a novel and improved heat conserving mechanism for furnaces which shall ensure safety in the operation of the furnace and which can be installed in any of a large number of standard heating systems without interference with the operation of the usual safety switches, limit controls and the like, to provide an electrically actuated mechanism of this character which shall consume a minimum of electric power and which shall ensure against wasteful "flare starts of the oil burner or gas burner during the period that the ambient temperature at the thermostat which controls the mechanism, e. g. a room thermostat, hovers closely to the degree for which the thermostat is set to start the burner; and to obtain other advantages and results that will be brought out by the following description in conjunction with th accompanying drawings in which:

Figure 1 is a schematic side elevational view of a house heating furnace with portions broken away and shown in section for cleamess in illustration.

Figure 2 is a combined enlarged side elevational view of the heat conserving mechanism embodying my invention and a wiring diagram.

Figure 3 is a top plan view of the mechanism shown in Figure 2 with portions broken away and shown in section.

Figure 4 is a fragmentary transverse vertical sectional view on the line 4-4 of Figure 2.

Figure 5 is a combined side elevatlonal and sectional view taken on the line 5-5 of Figure 2, and

Figure 6 is a vertical longitudinal sectional view taken on the line 6-6 of Figure 3.

For the purpose of illustrating the principles of the invention, I have shown it in conjunction with a known type of house heating furnace A which includes the usual combustion chamber I from which leads an outlet flue 2, and a heating unit which is shown as comprising an oil burner which includes an electric motor 3, a blower 4, a fuel supply nozzle 5 and electric ignition wires 8.

The apparatus for conserving heat includes-a damper 1 which is in the form of a disc pivotally mounted along a diametral line on a rod or shaft 3 which extends transversely of and is rotatably mounted in the flue 2, so that the damper in one position as shown in dotted lines in Figure 2 and in solid lines in Figure 3 may entirely close the flue or in another position as shown by dotted lines in Figure 3 may open the flue. A stop lug 3, preferably is provided in the flue to limit closing movement of the damper.

One end of the rod or shaft 3 projects from the line and has rigidly connected thereto a bell crank lever l3 one arm of which has a pin and slot connection II with a lever l2 which is pivotally mounted intermediate its ends at 13 on a supporting plate I4 which is mounted in any suitable manner on the flue as by straps l 5. The end of the lever i2 opposite the bell crank it has a pin and slot connection It with the armature ll of a solenoid l3 of an electromagnet which is also fixedly mounted on the supporting plate i4. With this construction the parts normally are in the position shown in Figure 2 and when the solenoid i3 is energized the armature l1 will be pulled downwardly and swing the lever 12 so as to rotate the bell crank lever i3 and swing the damper 1 into flue-openin position.

In accordance with the invention, as the damper 1 is moved into the open position, a timing mechanism is brought into operation to control starting of the motor 3 of the heating unit a predetermined time after the damper 1 has been moved into full open position. I have shown this mechanism as comprising a timing device which includes a casing B that has two chambers l9 and for containing a fluent substance and having a restricted passage 2| connecting them so that said substance may flow at a predetermined rate from one chamber to the other. More specifically the casing 13 is in the general form of an hour glass and the fluent substance 22 is a finely divided material, such as tiny glass beads or sand, which is responsive to the action of gravity.

The casing B is shown as tiltable or revoluble about a horizontal axis, for example on trunnions 23 that are iournaled in bearings 24 and 25 on the supporting plate l4. One end wall of one chamber, in the present instance the chamber 23, is in the form of a flexible diaphragm 2B, for example a piece of closely woven fabric which is impermeable to the fluent substance, said diaphragm normally resting on a substantially rigid plate 21 which is yieldably mounted on the easing B by tension springs 23.

The casing is tilted by a reciprocating rack bar 23 which is mounted on guides that are secured to the support plate l4 and meshes with a, pinion 3i rigidly connected to one of the trunnlons 23. One end of the rack bar 29 has a pin and slot connection 32 with the arm of the bell crank lever Ill opposite that which is connected to the lever i 2. Normally the casing B will be positioned with the diaphragm-containing chamber 20 uppermost but with the fluent substance in the lower chamber i9, as shown in Figure 2, and when the damper I is moved by the lever l2 from the closing position shown in Figure 2 to the open position, the casing B will be tilted to locate the diaphragm chamber 20 beneath the chamber l9 as shown in Figure 6. When the diaphragm chamber is in the lower position as shown in Figure 6, the fluent substance will flow by gravity from the upper chamber l9 onto the diaphragm 23 so as to force the plate 21 downwardly and close a normally open electric switch 33 so as to start the motor 3 of the heating unit as will be more fully described Also, in accordance with the invention, means is provided for returning the damper I to closed position and also to return the casing B of the timing device to its normal position after the heating unit has ceased operation. As shown. this means includes a link 34 which is pivotally connected at one end to the lever 12, preferably by the pivotal connection i8, and has a downwardly facing shoulder or hook 35 to cooperate with a hook or finger 35 on a lifting slide 31 that is reciprocably mounted on guides 33 on the supporting plate i4 and is connected to a flexible connector 39 which passes over guide pulleys 40 and is wound on a drum 4! which is mounted on a shaft 42 extending transversely of and rotatably mounted in the flue 2 and is actuated by a helical bimetallic thermostatic coil 43 one end of which is in fixed relation to the flue while the other end is rigidly connected to the shaft 42.

When the combustion gases in the flue 2 are relatively cool, i. e. when the heating unit is not operating, the thermostatic coil 43 will hold the lifting slide 31 in about the position shown in Figure 2, but the slide preferably normally is influenced by a light spring 44 against the action of the thermostatic coil. When the coil becomes heated, i. e. when the heating unit is operated, the shaft 42 will be rotated so as to allow the lifting slide 31 to descend.

The link 34 normally is actuated by a spring 43 toward the lifting slide but is limited in its movement in that direction by a stop stud 4511 on the supportin plate.

In operation of this portion of the apparatus, when the electromagnet l1, l8 operates the lever l2 to open the damper 1, the link 34 is pulled downwardly from the position shown in Figure 2. Shortly after the operation of the heating unit is started through closing of the switch 35 by the diaphragm 26 of the timing device, the thermostatic coil 43 will permit the lifting slide 31 to descend and the lower end thereof will eventually engage a cam surface 41 on the link 34 so as to temporarily swing the link away from the lifting slide and thereafter permit the link to return with its shoulder 35 in position to be engaged by the hook 36 when the latter rises.

After the operation of the heating unit has ceased, the cooling" gases in the flue 2 will slowly cause the thermostatic coil 43 to contract andwind the flexible connector 39 on the drum 4| so as to raise the lifting slide 31 and at the same time elevate the link 34 and the lever i2 and the armature 11 of the electromagnet. At the same time, the damper 1 will beclosed. When the damper has been closed, and after ample time has elapsed for complete purging of the furnace, the cam 41 on the link 34 will engage the stud 45a and push the shoulder 35 off the hook 36 of the lifting slide, whereby movement of the lever l2 and magnet armature will be stopped. The lifting slide, however, may continue to rise.

It will thus be seen that the damper 1 will be closed automatically and the casing B of the timing device will be inverted or returned to its normal position within a predetermined time sufficient to permit complete purging after the heating unit has ceased operating.

The diaphragm-containing chamber 20 which has the fluent substance therein is thus swung into its upper position and within the next few minutes the fluent substance will have returned by gravity to the chamber l3.

The operation of the electromagnet l1, -l3 and the control of the motor of the heating unit by 16 the timing device may be effected in many diiferent ways. For the purpose of illustration I have shown my invention combined with a known system of oil burner control which utilizes the Mercoid Pyratherm." The master controller is shown as consisting of a known type of room thermostat 46 which is connected in circuit with the secondary 41 of a transformer which provides a low voltage in the circuit immediately controlled by the room thermostat. The secondary coil 41 of the transformer cooperates with the primary coil so that when the room thermostat closes, the secondary coil moves with respect to the primary -coil to tilt the mercury switch 49 which is in circuit with the heating unit motor 43 to close that circuit. The usual safety switch 50 which is controlled by a bimetallic thermostat in the outlet flue is connected in circuit in the usual manner as is also a switch which controls the ignition circuit.

In accordance with my invention, even though the motor switch 49 and ignition switch 5! are closed, the motor of the heating unit and the ignition spark cannot start until the timing device included in my invention closes the switch 33. To effect this result the normally open switch 33 is interposed in the motor and ignition circuit so that said switch and the switches 5| and 49 must be closed before the motor can be energized. A normally closed switch 52 is connected in circuit with the solenoid l8 of the electromagnet so that when the room thermostat 48 closes its circult, the solenoid is first energized and the lever It is swung to open a damper l and at the same time rotate the casing B of the timing mechanism from the position shown in Figure 2 to the position shown in Figure 6. Thereupon the fluent substance in the timing device will fall upon the diaphragm 26 and after a predetermined quantity of the substance has descended. which will require a predetermined amount of time, the diaphragm 26 will be forced downwardly and cause the plate 21 to close the switch 33, whereupon the motor of the heating unit will be started. After the casing B of the timing device is almost completely rotated into proper position, a stud 53 thereon engages the switch 52 so as to open it and cause deenergization of the solenoid it. At the end of said rotation of the casing, another normally closed switch 54, which is connected in circuit with the room thermostat, will be opened. A switch 55, which is also connected in circuit with the room thermostat and in parallel with the switch 54, will be closed after a predetermined time interval and simultaneously with the switch 33 so as to return the system under control or the room thermostat that was briefly interrupted by the opening of the switch 54. The switch 54 is required in the particular system because without it and during the period when the furnace is without tire; that is, between the closing of the room thermostat and the starting of combustion in the heating unit, the electrical safety unit of the Pyratherm would open the entire circuit prematurely and require manual resetting. The

switch 55 is required to close the circuit previously opened by switch 54 through the room thermostat, so that operation of the motor can be under control of the room thermostat thereafter, as it ordinarily would without the inclusion of the timing switch 33. The opening of the room thermostat circuit by the switch 54- deenergizes the circuits in the same way as does the room thermostat switch 48 which is normally opened, so no safety shutdown need occur.

During operation of the heating unit, the thermostat 33 will have caused the lifting slide 3? to descend into the position to engage the shoulder 35 of the link 34, in readiness to close the damper and reset the timing device after operation of the heating unit has ceased.

When the room thermostat has been satisfied, that is, when the ambient temperature at the room thermostat reaches the temperature for which the thermostat is set to shut off the heating unit, the room thcrmostatwill be opened so as to open the circuit through the secondary of the transformer, whereupon the latter will move to operate the motor switch 49 and open the motor circuit. Within a short time after the heating unit has stopped, the cooling gases in the flue will cause the thermostat 43 to contract and, through the slide 31 and link 34, swing the lever 12 to close the damper I and at the same time rotate the timing device casing B into its normal position, whereby the apparatus is ready for the next call for heat from the room thermostat 46.

With this construction, it will be seen that the heating unit cannot be started until adequate time has elapsed for the purging of the furnace, and that the escape of thehot gases will be restricted by the damper 7 within a period of time after the heating unit has stopped operating which is short, but at the same time adequate to permit the escape of all combustible or objectionable gases before the damper is closed.

With the construction so far described, it will be observed that should the room thermostat 46 close shortly after the conclusion of the firing period, as by a sudden cold draft in the vicinity of the thermostat, such closing would cause the solenoid l1, Hi to pull down on the lifting link 31 which, at the same time, might be moving upwardly under the influence of the bimetallic coil 43. In other words, it is possible that the link 34 might be interlocked with the lifting link 31 and the solenoid could be exerting a downward influence at the same time that the bimetallic coil 43 was exerting an upward influence; and under such conditions, the solenoid l8 might be burned out. To avoid this, a normally closed thermostatic switch 62 may be connected in series with the'solenoid l8 and the switch 52, and constructed to open the circuit through the solenoid a short time, three to five seconds, after the solenoid has been energized, said thermostatic switch 62 then resetting itself within a certain period of time.

The structure of the switch 62 may be as desired, but is shown as including a bimetallic arm 63 which is fixedly mounted at one end on a suitable stationary support 84 and has a contact point 65 at its other end which cooperates with a stationary contact point 68. A coil 61 of high resistance wire surrounds the bimetallic arm 63 and has one terminal connected to the switch 52 and the other terminal connected to the contact point 65. Normally, the contact points 65 and 66 are in engagement with each other so as to close the switch, but upon closing of the room thermostat 46, the current flowing through the switch 52 and the solenoid It will cause the coil 61 to heat the bimetallic arm 33 so that the latter is flexed to move the contact point 65 out of engagement with the contact point 66 and thereby break the circuit through the solenoid. After a certain period of time, the bimetallic arm 63 will cool and return to its normal position to close the switch.

Another feature of my invention is an autoaaoaecs matic control for a barometric damper which is usually installed in the outlet flue. As shown, this barometric damper includes a plate 55 pivotally mounted in an opening 51 in the side of the flue and at the side of the damper I opposite the combustion chamber, the plate being pivotally'inounted at 53 so as to normally swing by gravity into closed position. In usual operation, this damper is closed when the heating unit is not operating, and is automatically pulled open by the draft while the heating unit is in operation. To hold the plate positively in closed position so as to prevent a draft and loss of heated basement air through the flue while the heating unit is out of operation, I have shown the rack bar 29 as provided with an extension 59, the end of which, when the apparatus is in normal position, abuts the plate 56 to prevent it opening under the influence of gravity and barometric differentials. The extension 59 is of such length and shape that when the apparatus has been actuated upon starting of the heating unit, the end of the extension is moved away from the plate 56 so that the latter may swing open under influence of the draft, as shown by dot-and-dash lines in Figure 3. Preferably the end 59 is curved or has a cam surface so as to tend to press the damper plate 55 into closed position as the damper I is closed.

While I have shown and described the invention more or less schematically, it will be understood that this is primarily for the purpose of illustrating the principles of the invention and that many modifications and changes in the details of construction of the apparatus can be made within the spirit and scope of the invention. For example, the switches 33, 52, 54 and 55 may be of a known type which can be opened or closed as the case may be upon application of light pressures, e. g., of the order of /2 ounce, and upon travel of the operating arm at distances of the order of .003". If desired, the moving parts of the apparatus mounted on the supporting plate 14 may be enclosed in a cover it.

The switches may be mounted as desired, and it will occur to those skilled in the art that the switches 33 and 55 might be mounted directly on the casing 13 instead of upon separate brackets as shown. Moreover, it will be understood that the timing device per se may be utilized for other purposes than the control of heating apparatus. My invention may also be combined,

with proper circuit changes which are within the skill of the art, with other types of oil burner or gas heater controls than the "Pyratherm" control hereinabove described.

What I claim is:

1. The combination with. heating apparatus including means providing a combustion chamber, a heating unit within said chamber, an outlet flue for discharging combustion gases from said combustion chamber, and a master controller, of a damper located in said outlet flue and controlling flow of said combustion gases from said combustion chamber through said flue, and mechanism controlled by said master controller for moving said damper to full open position, a timing device actuation. of which is initiated by said mechanism for starting said heating unit a predetermined time after said damper has been fully opened, means including said master controller for stopping operation of said heating unit, and means responsive to temperature in said outlet flue upon a drop in said temperature below a predetermined degree due. to stoppage of said heating unit for closing said damper after said heating unit has ceased operation.

2. The combination with heating apparatus including means forming a combustion chamber, a heating unit within said chamber, an outlet flue for discharging combustion gases from said combustion chamber, and a master controller, of a damper located in said outlet flue and controlling'flow of combustion gases from said combustion chamber through said flue, means controlled by said master controller for moving said damper to full open position, a timing device operation of which is initiated by said master controller when said master controller operates to open said damper for directly controlling starting of said heating unit a predetermined time after said damper has been fully opened, means including said master controller for stopping operation of said heating unit, and means responsive to temperature in said flue for resetting said timing device after said heating unit has ceased operation.

3. The combination with heating apparatus including means forming a combustion chamber, a heating unit within said chamber, an outlet flue for discharging combustion gases from said combustion chamber, and a master controller, of a damper located in said outlet flue and controlling iiow of combustion gases from said chamber through said flue, means controlled by said master controller for moving said damper to full open position, a timing device operation of which is initiated by said master controller when said master controller operates to open said damper for directly controlling starting of said heating unit a predetermined time after said damper has been fully opened, means including said master controller for stopping operation of said heating unit, and means responsive to temperature in said flue for res tting said timing device and for closing said damper a predetermined time after said heating unit has ceased operation. TED J. MACKAY.

REFERENCES CITED The following references are of record in the flle of this patent:

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